1. Field of the Disclosure
The present disclosure relates to drill bits used in the oil and gas industry. Specifically, the disclosure relates to an improved method of manufacturing earth-boring bits for drilling earth formations.
2. Description of the Related Art
Drill bits are used in the oil and gas industry to drill earth formations in the exploration for gas and oil. FIG. 1 depicts a drilling rig which incorporates a drill bit 10. Drill bit 10 is connected to the bottom of a drill string 13 to drill a wellbore 15. The drillstring may be controlled by surface equipment configured to rotate the drill string, apply downward force (i.e., weight on bit) to the drill bit to penetrate the earth formation and supply drilling fluid to drill bit 10 by pumping the fluid through a bore of the drill string. Because a variety of earth formations are penetrated in the pursuit of oil and gas, several different types and configurations of drill bits are used. These drill bits are typically grouped into two categories, drag bits (also known as shear cutter bits) and roller cone bits.
Shear bits are drill bits that cut the earth's formation by primarily scraping the earth formation as they are rotated by a drillstring and/or a downhole motor in a drilling operation. Shear bits include those having cutters (sometimes referred to as cutter elements, cutting elements or inserts) attached to the bit body. For example, the cutters may be formed having a substrate or support stud made of carbide, for example tungsten carbide, and an ultra hard cutting surface layer or “table” made of a polycrystalline diamond material or a polycrystalline boron nitride material deposited onto or otherwise bonded to the substrate at an interface surface. The shear bit may be fixed to the drill string which is rotated so, as the drill string rotates, the bit also rotates to cut into the earth formation. Shear bits typically do not have any moving parts upon the bit itself, only the bit body moves from the rotation of the drill string.
In contrast, roller cone bits are drill bits having cones rotatably mounted onto journals. The roller cone bit typically includes a bit body having at least one journal, in which a cone is mounted thereupon and allowed to rotate. As the bit body is rotated by the drill string and/or downhole motor, the cones may rotatably contact the earth's formation. A plurality of cutting elements arranged on the roller cones crush and scrape the earth's formation as the bit is rotated. Although both types of drill bit may be applicable to embodiments disclosed herein, for purposes of brevity, only shear bits will be discussed from this point forward.
An example of a shear bit having a plurality of cutters with ultra hard working surfaces is shown in FIG. 2. A shear-type drill bit 10 includes a bit body 12 and a plurality of blades 14 formed on bit body 12. Blades 14 may be separated by channels or gaps 16 that enable drilling fluid to flow between and both clean and cool blades 14 and cutters 18. Cutters 18 may be held in blades 14 at predetermined angular orientations and radial locations to present working surfaces 20 at a desired back rake angle against a formation to be drilled. Typically, working surfaces 20 may be generally perpendicular to an axis 19 and side surface 21 of a cylindrical cutter 18. Thus, working surface 20 and a side surface 21 may meet or intersect to form a circumferential cutting edge 22.
Orifices are typically formed in the drill bit body 12 and positioned in the gaps 16. The orifices may be adapted to accept nozzles 23 and allow drilling fluid to be discharged through the bit in selected directions and at selected rates of flow between the cutting blades 14 for lubricating and cooling drill bit 10, blades 14 and cutters 18. The drilling fluid may also clean and remove the cuttings as the drill bit rotates and penetrates a geological formation. Gaps 16, which may be referred to as “fluid courses,” may be positioned to provide additional flow channels for drilling fluid and to provide a passage for formation cuttings to travel past the drill bit 10 toward the surface of a wellbore (15 of FIG. 1).
Shear bits may be further grouped into several categories including steel body bits and matrix body bits. Steel body bits traditionally have bit heads machined from solid piece of metal, typically steel. Upon completion of the machining, the bit head may be mated and assembled to a bit shank. Typically, the bit heads include the cutting elements and the bit shank includes a connection (typically threaded) to the remainder of the drill string. Hydraulic chambers (nozzles, passages, plenums, etc.) may be located in both the head and shank portions so that once assembled, a hydraulic network exists in the assembled drill bit. Typically, shear bits use polycrystalline diamond compact (“PDC”) cutters or some other type of ultra hard and wear resistant material to shear the earth formation.
In contrast, matrix body bit heads are typically constructed using a powder metallurgy manufacturing process. A cutter head mold of the desired bit head shape is constructed and filled with matrix powder a binder agent, and at least one rigid (e.g., steel) structural element. Next, the mold is placed in a furnace to allow the binder to melt and infiltrate the matrix powder (i.e., a sintering process). As the binder infiltrates the matrix powder, a solid metal casting is formed and fused to the rigid structural element. Thus, once the sintering process is completed, a powder metallurgy-created bit head remains that may be attached to a steel (or other material) bit shank in a manner similar to the steel body bits. Two types of matrix body bits include bits incorporating PDC cutters and bits incorporating natural diamonds impregnated in the matrix powder to scrape the formation. Bits may be manufactured with combinations of the two matrix bit body technologies.
Regardless of the type of shear bit created, the manufacturing process may include a step whereby the bit head crown (either machined or molded) is attached to the bit shank so that a completed bit is constructed. Formerly, the bit heads and the bit shanks may have been formed with corresponding service threads so that they could be threaded together at final assembly. Threaded bit shanks and bit heads had the additional advantage in that they allowed for the attachment of fixtures and tooling to the bit components at various stages of manufacture. For example, a lifting jig may have been threaded to the service threads of a bit shank to assist in lifting and carrying an unfinished bit shank through a process line. Similarly, service threads (e.g., formed upon the rigid structural element of a matrix head PDC bit) of a bit head could have been used to secure a bit head during sintering, transport, or assembly of cutters and/or nozzles.